Nowadays, liquid crystal displays (LCDs) are becoming the main stream of displaying technology, and are being widely applied to various electronic products, such as a mobile phone, a PDA, a digital camera, a computer screen, a notebook screen and the like. A backlight module is one of the crucial components being a deciding factor of the quality of an LCD. Generally, the illuminating light source of the backlight module is implemented by an electro-luminance (EL) element, a light emitting diode, or a cold cathode fluorescent lamp. Among the above three light sources, LEDs are widely utilized in small LCD devices due to the small volume, light weight and excellent controllability.
LED backlight modules can be classified into types of direct-lit backlight modules and edge-lit backlight modules according to the disposal of the light sources thereof. In a direct-lit backlight module, LED dice are evenly disposed under a liquid crystal panel and server as the light sources, and thereby uniformly transmitting the backlight all over the screen.
FIG. 1 is a schematic diagram showing an application example of a conventional direct-lit LED backlight module. For purpose of simplicity and clarity, some components are omitted in the drawings. As shown, in an LCD, a light source constituted by an LED matrix 20 is disposed under a liquid crystal glass 10. The LED matrix 20 comprises a number of LED dice 201 arranged in columns and rows. The liquid crystal glass 10 comprises liquid crystal being sandwiched therein. The liquid crystal glass has been used in various applications. Since it is not the focus of the present invention, the details thereof are omitted herein.
In such a structure, the LED dice 201 are arranged under the liquid crystal glass 10 to provide the liquid crystal glass 10 with light illumination. Accordingly, local dimming can be easily accomplished. In this example, the liquid crystal glass 10 is divided into regions A1 to A6, B1 to B6, C1 to C6 and D1 to D6. By controlling the LED dice corresponding to the respective regions, the local dimming of each region can be achieved. The LED matrix 20 can transfer the heat thereof directly to a back plate (not shown) to accomplish heat dissipation. However, a great quantity of the LED dice are necessary for such a structure, and more electrical power is consumed thereof. Furthermore, the finished LCD will have a greater thickness since there is a layer of the LED matrix 20.
FIG. 2 is a schematic diagram showing an application example of a conventional edge-lit LED backlight module. As shown, LED light bars 22, 24, are disposed at the two long sides of a liquid crystal glass 11 respectively. Taking the LED light bar 24 as an example, the LED light bar 24 comprises a plurality of LED dice 241. In this example, the LED light bar 22 is used to control the luminance of each of the regions A1 to A6 of the liquid crystal glass 11; the LED light bar 24 is used to control the luminance of each of the regions B1 to B6 of the liquid crystal glass 11. The edge-lit LED backlight module requires fewer LED dice. However, in such a structure, the heat generated by the LED light bars 22, 24, needs to be transferred to the back plate through a metal substrate (e.g. an aluminum substrate) to dissipate the heat. The accomplishment of heat dissipation is inconvenient and the effect thereof is unfavorable. Further, the local dimming of the respective regions is likely to be interfered by each other.
Therefore, an improved backlight module is required to solve the existing problems of the current technique.